Most traditional fossil fuel, nuclear, and solar heat-driven power plants typically utilize water (R-718) as a primary phase change working fluid for cooling purposes. In HVAC applications, a refrigerant, such as R-410A, R134A, R744 CO2, or the like, is typically utilized as a phase change working fluid for cooling purposes. Typically, at least one of water and a refrigerant is utilized as the working fluid in other types of heat rejection systems operating with a working fluid, although simple heat rejection may sometimes be accomplished through a flat plate, or the like.
Water is readily available and inexpensive, and has therefore been traditionally utilized in such heat-driven power generation facilities, where relatively large amounts of water are required in the primary working fluid closed-loop. Typically, the water is pumped into and through a boiler, where the water is vaporized and superheated to a high pressure. The high-pressure steam may power one or more turbine/generators which extract mechanical energy from the steam, thereby reducing the pressure and temperature of the steam. Some of the hot steam is typically used to pre-heat water returned to the boiler, while the remaining steam is cooled and condensed back into a liquid. Some or all of the condensed water may be pumped back to the boiler to repeat the cycle.
With water as the working fluid in the primary power generation closed-loop portion of the power plant, under normal atmospheric pressures (1 bar, or about 14.5038 psi) as an example, about 970.4 BTUs are required to phase change one pound of water into steam, and the same approximate 970.4 BTUs are required to phase change the steam back into one pound of liquid water. Energy is required to effect the two respective phase changes, but the temperature of the water is not materially affected during the change in phase. Rather, during a change in phase, typically only the state of the water (i.e., liquid or vapor form) is affected. Once the working fluid is in a water only state/phase, however, only 1 BTU per pound of water under normal atmospheric pressures is needed to change (i.e., increase or decrease) the temperature of the water by 1 degree F.
Consequently, to solely effect the two necessary phase changes of water (water into a vapor/steam and steam into water), if operating under normal atmospheric pressures, about 1,940.8 BTUs of energy must be provided per one pound of water.
Refrigerants other than water may be used as the primary phase change working fluid in common HVAC heating and cooling applications (as well as in some geothermal power production systems, in some solar heat power production systems, in some waste heat power production systems, in other various types of heat-driven power production systems, and the like). In such non-water refrigerant working fluid applications, working fluid phase change temperatures, at the same normal atmospheric pressure for example, typically require less BTUs than water to effect a phase change, which may be advantageous for a particular application.
However, regardless of the working fluid utilized in power production or cooling applications, generally, about the same amount of BTU energy required to vaporize the working fluid utilized is also required to condense the same working fluid back into a liquid state. Condensing and liquefying a working fluid is effected by removing heat from the vapor phase working fluid. After the BTU energy necessary to condense the working fluid is supplied, far less BTU energy is then needed per pound to subsequently cool the liquefied refrigerant working fluid below it's condensation point (herein referred to as sub-cooling). For example, under normal atmospheric pressures, it takes about 970.4 BTUs to condense 1 pound of water, but then it only takes about 1 BTU to further cool the same 1 pound of water per 1 degree F.
Cooling work for phase changing and for sub-cooling a working fluid to temperatures below the working fluid's condensation point requires the expenditure of BTU energy. Such cooling work is typically provided by exchanging heat from the primary hot working fluid with at least one of cooler air, with a separate cooler water source (such as a river, a lake, well water, ocean water, or the like); with another cooler working fluid (such as a refrigerant to water heat exchanger in a geothermal water-source heat pump system); and/or with an evaporative cooling system, where water is typically sprayed onto a hotter working fluid container/pipe where the cooler water absorbs and removes enough BTUs from the primary working fluid to evaporate the sprayed on water. Heat is naturally transferred from a warmer working fluid to a cooler surrounding environment via Fourier's Law, as heat naturally travels to cold.
While in most power production systems, attention is generally primarily afforded to a cost-effective way to provide heat to vaporize and raise the temperature of the primary working fluid to a desirable level (raising the temperature above the vaporization point is herein referred to as superheating), it is also very important to provide a cost-effective and environmentally friendly way to condense and sub-cool the primary working fluid to a desirable level. Generally, for example, the cooler the closed-loop working fluid in a power plant, the greater the temperature differentials and the greater the amount of power that can be generated. Similarly, generally in an HVAC application, the greater the closed-loop working fluid temperature differentials, the greater the amount of cooling work that can be provided.
Traditional power plant cooling methods can have adverse environmental impacts. For example, using river and/or lake water to condense and/or sub-cool the closed-loop water working fluid in large power plants in the summer can result in the river and/or lake water becoming so warm that it kills native fish and/or other aquatic life, or in becoming so warm so that it enhances the quantity of zebra muscles, which can clog up fresh water intakes, or the like. Also, as another example, vaporized salt water from seawater-cooled power plants can impair vegetation and/or farmland for miles around such a power production facility. Further, as natural river and/or lake water naturally heats up in the summer, power plant operational temperature differentials deteriorate and power production abilities decrease.
Instead of using an exterior water source to cool closed-loop water working fluid in a power plant, as an example, condensing and/or cooling the primary closed-loop water working fluid with air can be expensive, requiring large arrays of finned tubing, or the like, often with parasitic power-consuming fans so as to increase airflow and the cooling effect. Also, as outdoor air temperatures rise during the summer (just as with rising natural water temperatures when water is used for cooling), decreases in the primary working fluid temperature differentials result, and cooling abilities correspondingly disadvantageously decrease. This, in turn, results in more cooling equipment and/or more fan power being required, and/or in lower than optimum design power output. When design levels of working fluid cooling cannot be attained, normal operational design levels of power production in power plants, and normal operational design levels of cooling abilities in HVAC systems, typically cannot be supplied.